1. Field of the Invention
The invention relates generally to roller bearings, and more particularly to roller bearings having components that precess or index when such roller bearings are used in oscillatory applications to cycle those components through the load zones of the bearings.
2. Reference to Prior Art
Examples of self-aligning angular contact roller bearings are provided in U.S. Pat. No. 2,387,962 issued Sep. 28, 1942, U.S. Pat. No. 2,767,037 issued Oct. 16, 1956, and U.S. Pat. No. 4,557,613 issued Dec. 10, 1985. In each of those patents the illustrated roller bearing includes an inner ring that provides a substantially spherical inner race surface, an outer ring having a pair of outer race surfaces with convex curvatures, and a pair of oppositely axially inclined rows of symmetrical, hourglass-shaped rollers. Another example of an angular contact roller bearing is illustrated in U.S. Pat. No. 3,912,346 issued Oct. 14, 1975. That roller bearing includes oppositely axially inclined rows of symmetrical, barrel-shaped rollers.
The foregoing roller bearings also include roller cages or retainers to separate, guide and position the rollers in each row. Each of the retainers includes sets of axially oppositely extending webs or prongs that extend parallel to the axis of the roller bearing. Those prongs fully circumferentially separate the rollers and limit the number of rollers that will fit in a roller bearing.
When in service, loads exerted on a bearing unit such as one of those described above are typically carried by only one part of the bearing unit at a time, that part being referred to as the "load zone". If the bearing unit is used in an oscillatory application it is desired that the rollers in the bearing precess or index so that they are cycled through the load zone. Cycling the rollers results in utilization of the entire race surface of each of the rollers to extend rolling contact fatigue life. Cycling the rollers also redistributes lubrication within the bearing unit which in turn reduces fretting damage and improves the bearing unit's resistance to raceway corrosion.
When the foregoing roller bearings are used in oscillatory applications roller precession is negligible, and while failures in those bearings can be inner ring-related, such as by spalling on the inner race surface for example, or to a lesser extent outer ring-related, the majority of failures are roller-related. To improve aspects of performance of a roller bearing used in an oscillatory application it is known to remove the retainer from that bearing. Removal of the retainer frees space for additional rollers so that loads are carried by a greater number of rollers occupying the load zone. Also, Applicants have determined through testing that the rollers in retainerless roller bearings experience irregular or inconsistent precession (i.e., rollers do not always precess in the same direction or by the same amount) which may bring different rollers into the load zone.
It is also known that improved performance of a roller bearing to be used in an oscillatory application can be achieved by replacing the above-described retainer with a "precessing retainer" in which the webs or prongs are circumferentially inclined. In one known precessing retainer design the prongs are circumferentially inclined at an angle of about 4.degree. to provide an imbalanced amount of skew to the rollers. When the angle of oscillation of the bearing is sufficiently large (i.e., at least 2.degree.-3.degree.) the rollers skewed by the precessing retainer tend to precess or index to continually cycle rollers through the load zone. This reduces the occurrence of roller-related failures and thereby increases the life of the bearing.